Multiconductor cable



July 4, 1961 N. R. LAY

MULTICONDUCTOR CABLE Filed April 6, 1959 FIG.

3 Sheets-Sheet 1 Norman R Lay INVENTOR.

July 4, 1961 N. R. LAY 2,991,328

MULTICONDUCTOR CABLE Filed April 6, 1959 3 Sheets-Sheet 2 Norman R. Loy

INVENTOR.

BY AGENT July 4, 1961 N. R. LAY

MULTIcoNDUcToR CABLE Filed April 6, 1959 3 Sheets-Sheet 3 Norman R, L uyINVENTOR.

BY jQ/fcw AGENT United States Patent() 2,991,328 MULTICONDUCTOR CABLENorman R. Lay, Arlington, Tex., assignor to Chance Vought Corporation, acorporation of Delaware Filed Apr. 6, 1959, Ser. No. 804,177 14 Claims.(Cl.17472) This invention relates to multiconductor cables and theirconstruction and more particularly to a relatively rigid multiconductorcable and a method for making the same.

Where electrical harnesses or cables comprising grouped, generallyparallel electrical conductors are used in aircraft or other structures,particularly where vibration and other factors tend to produce relativemotion between the group of conductors and other items on which or nearwhich they are mounted, chang of wires in the group or bundle is aproblem which must be surmounted. Where, as has been the commonpractice, each Wire in the group is provided with an electricalinsulating layer which lies immediately over the conductor and, inaddition to this, a fabric or other layer provided for protectionagainst chafing and which overlies the first, insulating layer, theouter, protective layers of the several wires, one on each wire in thegroup or bundle, add up to a considerable weight and also greatlyincrease the bulk of the bundle.

It previously has been proposed that the outer, abrasion-protectivelayers of the wires be left olf and the entire bundle inserted into aprotective casing. Thus, it has been the common practice to draw abundle of wires through a flexible casing or sleeve made of vinylplastic or some other dielectric material. The outer sleevings employedhave themselves been subject to an undesirable extent to chang andabrasion, and because harnesses made with flexible sleevings tend to sagand are easily fdeected, they must be clamped at relatively closeintervals to the structural items on which they are mounted, and, toprevent chang, adequate and relatively wide clearances must be leftbetween them and adjoining items against which they might be deflectedunder vibration or Iother conditions.

In addition, the drawing of a large group of conductors., 'some or allof which might be quite fragile, through a relatively long protectivesleeve is a time-consuming, difficult operation which tends to stretchthe wires, and there are distinct limitations upon the compactness anddensity which can be attained in a bundle of wires so protected.

in making a multiconductor cable of minimum size yand weight, the amountof metal of the conductors and the amount of insulating materialsurrounding them may 'both be reduced to the minimum amounts givingsutlic'ient electrical power-carrying capacity and adequately preventingshorting vand arcing'between the conductors. ,A limit is reached whenthe wires become so small that excessive heating is produced undernormal loads or predictablc overloads, and this heating tends to destroyboth `the Wire and the insulating material about it. A lire hazard isattendant upon such a failure in a wire, and 'adjoining wires are aptalso to be damaged. Meanwhile, 'the deleterious effects upon them ofoperation in `high- =temperature environments have tended to limit theusefulness of electrical cables.

Parallel, individual conductors have previously been :cast into asingle, vhomogenous block or strip or insular zing material, but thismode of construction is of little or no advantage in reducing weight orcross-sectional 'area of the harness because it is not practicallypossible to space wires of any considerable length very closely dogetherwithout having some of them contact or cross Aeach other andconsequently entering into a short-cir- .cuited relation which is madepermanent when the wires p ICC are cast into the insulating material.For this reason, the wires must be spaced well apart, with added spacingfor safety; and a great weight and volume of insulating material must beused in making the solid block or strip into which they -are cast. Forreasons concerning their electrical properties and their producibility,the conductors which most often are used in electrical harnesses aremade of single or stranded wires of circular cross section. Even if thespacing of wires of circular crosssection could be controlled soreliably and well that the wires could be spaced so closely that theinsulation about each wire was, at its thinnest point, of the minimumthickness for preventing arc-over to an adjoining wire,

the embedding of the wires in a solid, common, insulating blockrequires, by its very nature, the lling of all of the spaces between theround wires and thus, of course, requires the use of a great weight ofinsulating material above that actually necessary merely for theinsulation of the wires.

A cable made of a plurality of wires cast into a single piece ofinsulating material tends to behave under tlexure, from vibration orother causes, as a single bar and does not have the advantages which, aswill become apparent, accrue to a multiconductor cable in which eachwire is slideable, with its insulating sheath, lengthwise of and againstadjoining wires. The same disadvantage may, and ordinarily does, appearin cables made of a large number of individually insulated wires pulledthrough a protective sheath: as more wires Vare introduced into a sheathof given diameter in an attempt to produce a highly compact cable,wire-to-wire friction becomes so high that the individual wires nolonger are slideable against each other within the sheath, and the cablebehaves as a solid, though not necessarily rigid, bar. This behaviorbecomes a defect where, for example, it causes the cable to display aresonance to mechanical vibrations and thus further aggravate theproblems of c hang, clamping, etc.

The sleevings through which bundles of wires have been pulled for makingjacketed multiconductor cables have been of round cross-section. Use ofjackets of such cross-section has been compelled by practicalconsiderations including the dificulties which would be encountered inpulling wires through a sleeve which, for example, had a rectangularcross-section, to the end that the bundle of wires would thoroughly fillthe jacket. Further, in case of a flexible jacket, the rectangularcrosssection is distorted by pressures of the wires and tends to becomeof circular cross-section as it becomes tightly lled with the wires. Inmany, probably in most, applications a multiconductor cable of circularcross-section is quite wasteful of space; for example, where it isstrung along one or more substantially liat surfaces, space would besaved (in most cases) if the cable were of rectangular cross-section.Ideally, of course, space would best be conserved by making thecross-section of the cable, at any point along its length, such as bestto tit against and among the other items with which it must beassociated.

`It is, accordingly, a major object of the invention to provide a rigidmulticonductor cable of improved low weight and volume.

Another object is to provide a rigid multiconductor cable which ispre-shaped to conform to surfaces against or near to which it is to `bemounted and which is accurately and stably locatable relative to suchsurfaces.

A further object is to provide a rigid multiconductor cable which issubstantially non-resonant to mechanical vibration and which requires a.minimum number of mounting points.

Yet another object is to provide a rigid multiconductor cable ofimproved resistance to heat and abrasion.

A still further object is to provide a multiconductor cable of improvedresistance to electrical overloading of individual wires in the cableand possessing a greater current-carrying capacity of the wiresindividually and as a whole.

Still another object is to provide a novel and eicient method for makinga rigid multiconductor cable of smaller size and lower weight thanpreviously practicable and of improved abrasion and heat resistances.

An additional object is to provide a rigid, multicenductor cable of highdensity and consequently low volume and which is substantiallywater-proof, air tight, and immune to the eifects of acids and bases.

Yet another object is to provide a high-density multiconductor cablehaving branches that are of one-piece, unitary construction with eachother and to supply a practical and efficient method for making thesame.

Still other objects and advantages will be apparent from thespecification and claims and from the accompanying drawing whichilustrates an embodiment of the invention.

In the dra-wing:

FIGURE 1 is a perspective view of a preferred embodiment of themulticonductor cable;

FIGURE 2 is an enlarged view in elevation of a segment of the cable inwhich portions of the cover have been removed to show the wires and thereinforcing plate;

FIGURE 3 is a cross-sectional view of the cable taken as at line III-IIIin FIGURE 1;

FIGURE -4 is a longitudinal sectional view taken as along the line andlooking in the direction shown by the arrows at IV-IV in FIGURE l;

FIGURE 5 is a cross-sectional view through several typical conductors ofthe cable shown in other figures;

FIGURE 6 is a plane view of a branched portion of the cable shown inFIGURE 1 in which some of the outer cover is removed to show the coverinterior and installation of an outer, flexible jacket at an opening ofthe cover;

FIGURE 7 is a side elevation of the cable portion shown in FIGURE 6, thecable branch being shown in a cross-sectional view taken as at VII--VIIin FIGURE 6;

FIGURE 8 is a perspective view of a harness of wires prepared forincorporation into a multiconductor cable such as shown in FIGURE l;

FIGURE 9 is a cross-sectional view taken as at IX-IX in FIGURE l0 andwith the male mold member shown not yet inserted into the female moldmember;

FIGURE 10 is a perspective view of the mold with the multiconductorparts being molded therein; and

FIGURE 1l is a longitudinal sectional view of the cable taken at an endof the cover.

With reference now to FIGURES 1 and 2. of the drawing, themulticonductor cable 10 compirses an elongated, tubular cover 11 throughwhich extends a plurality of elongated, individually insulatedconductors such as the wires 12. The ends of the wires 12 may beprovided with suitable terminals or connectors, such as, for instance,the multiconnector plugs or receptacles 13. Many electrical plugs,receptacles, terminals, and other suitable means for connecting thewires into electrical circuits in order that they may form parts ofcircuits are well known in the art and require no further explanation ordescription herein except to mention that they preferably should besmall and light as practically possible. Self-locking frictionalconnectors which have been ernployed with excellent results on the wiresand which offer good advantages of weight are those shown in the U.S.Patent 2,816,275, issued on December 10, 1957, to Kemper M. Hammell. Theouter shape of the cover 11, in the example shown, is rectangular at thelocation of the cross-section shown in FIGURE 3, but is by no meanslimited to the cross-sectional shape shown; for it may be made insquare, circular, oval, triangular, or still other cross-sectionalshapes as desired. Moreover,

the cover 11 need not be of one same cross-sectional 4 shape along allits length, and it is preferable that this shape be varied, inmanufacture of the cable, where and if this oiers a decisive advantageof giving it a predetermined cross-sectional shape which enables it tofit with best economy of space among or against items near or on whichit is to be mounted. The cover 11 similarly is curved or bent along itslength, as at 14, 15 (FIGURE 1), for shaping it to lie exactly along adesired routing through a computer cabinet, aircraft or missilecompartment, or other location within which it may be desired to lit itwith considerable exactitude.

As seen in FIGURE 3, the cover 11 has a wall 16 whose inner surfacedefines an inner volume or cavity which extends lengthwise within andthrough the cover from one of its ends 17, 18 (FIGURE 1) to the other,and this cavity is substantially lled with the wires 12. The elongatedconductors 20` (see FIGURE 5) included in the wires 12 are individuallyprovided, each one of them, with a separate insulating sheath 19. Thesheaths 19 of the wires 12 are ofcourse made of a dielectric material;and it is preferable that this material be a resilient plastic which hasa low coefficient of friction and which is free of adhesivecompatibility with the material of the outer cover 11 even at highoperating ternperatures or at temperatures which may be employed, aswill be described, for curing the outer cover. The multiconductor cable10 is better tted, because of details of its construction which willbecome apparent, than previous cables for operation in environments inwhich the temperature is very high; and where such an environment iscontemplated, the sheaths 19 of the conductors 20 should be made of amaterial whose electrical insulating properties do not break down athigh temperatures and which is not subject to physical changes such assoftening which could allow shifting of the conductors 20 within thesheaths 19 or result in `welding of one of the sheaths 19 to anothersheath 19 with which it is in contact or with the cover 11 where theparticular sheath 19 is one which contacts the latter. Meanwhile, it isdesirable that the sheath material employed, while possessing the otherqualities enumerated above, should be (at lea-st among the class ofresilient, dielectric materials) in itself a fair conductor of heat.

The wires 12 need not be all of the same size, and it is entirelypracticable to intermix wires which are, as shown in FIGURE 5, ofradically different'diarneters. If desired, some shielded or coaxialconductors such as the wire 21 may be included. The wire 21 may have anoutermost sheath 22 of material identical or similar to that of thesheaths 19. For simplicity, only wires 12 are spoken of hereinafter; butit will be understood that, where their presence is appropriate,reference is intended also to wires such as 21, and that still otherkinds of wires or equivalent may be included among the wires 12.

The specific material employed in the wire sheaths 19 may be variedaccording to the conditions under which the cable l10 will be expectedto perform. Materials generally preferred because of their superiorelectrical, thermal, and mechanical properties are thetetrafiuorethylene resins, marketed under the trade name of Teon by I.E. du Pont de Nemours Company of Wilmington, Delaware. Though notgenerally capable of withstanding as high a temperature as Teflon andnot possessing, for example, as extremely low a coeicient of friction asthe latter, materials entirely suitable for many applications are foundamong the silicone rubbers, and still other materials are satisfactory,for instance those presently used `for the insulating of electricalwires and listed in the U.S. Government Specification MIL- W-16878C(Navy) of April 3, 1958. As far as consistent with it having the otherdesirabilities noted herein, it is preferred that the material chosen beof the highest obtainable dielectric strength per mil of thickness sincethis permits the use of sheaths 19 of minimum thickness and closerspacing of the conductors 20; and

this aids in reducing the weight and overall size of the multiconductorcable 10. The thicknesses of the sheaths 19 must be great enough toprevent voltage breakdown Vbetween the conductors at the voltages orovervoltages they may reasonably be predicted to encounter in service ofthe cable 10.

The relationship of the conductors 20 and their sheaths 19 with eachother and with the wall of the cover 11 shown in the cross-sectionalview presented in FIG- URE 3 is generally typical along all the lengthof the cover. Substantially every sheath 19, in all its length withinthe cover 11, has intimate contact with adjoining sheaths 19, and allthe conductors 20 are confined to this contacting relationship bycontact of sheaths 19 of conductors 20 lying at the borders of the groupof wires 12 with the inner surface of the cover 11. The wires 12 arecompacted, i.e., made to lie very closely against each other as tightlyas is consistent with achieving an optimum relationsh'p between thedensity of the group of wires 12 and a desired degree of freedom fromlack of pressure-induced deformation of their sheaths 19 sufficient tosqueeze any sheath 19 such that it, together with the material ofadjoining sheaths 19, would not be thick enough to provide sufficientdielectric material between its conductor 20 and adjoining conductors20. The density of the group of wires "12 preferably is that at whichvirtually no space is wasted between the wires: all the space within theinterior volume of the cover 11 should be filled with wires 12 arrangedto lie as closely together and preferably with as much contact with eachother as their cylindrical cross-sections permit, thus reducing to aminimum the voids between them and hence making the Volume occupied bythe group as .A small as possible. Packing the wires 12 so tightly thatthe sheaths 19 are greatly attened or otherwise deformed and to asigni-cant extent made locally thinner by contact with each other is tobe avoided for the reasonsl given above. In practice, some suchdeformation mayfbe acceptable; but it must be kept within reasonablelimits, for excessive pressure-induced thinning of the sheaths 19 willdefeat a purpose of the invention. Since the wall thickness of thesheaths 19 is, to begin with, at (or near) a practical minimum, andsince the dielectric strength of a sheath 19 tends to be no greater thanthat at its thinnest point, compressing the wires 12 so tightly as, forinstance, to change their respective sheaths 19 from circular tohexagonal cross-section tends to defeat the invention and its object ofproviding a light-weight cable. Depending upon the voltages at which thewires 12' are to be used and upon the material of which the sheaths `19are made, there is a certain minimum thickness of sheath material whichmust interlie adjoining conductors 20 to prevent voltage breakdownbetween them. When a conductor 20 of circular cross-section is spacedfrom the nearest-approaching points of surrounding conductors 20 ofsimilar section by its own and other sheaths 19 whose combined thicknessbetween adjoining conductors equals this required thickness ofdielectric material, the lightest-weight, electricallyl effectiveinsulation of theA conductors 20 is effected by sheaths 19'of annularcross-section. To fill in, in effect, between these round sheaths untilthey were, for instance, hexagonal would be to add weight withoutincreasing the effective thickness of the insulation or adding to thedielectric strength between the wires 20, and hence is to be avoided.

The wires 20 thus are compactly grouped together within and forpractical purposes completely fill the inner volume of the cover 11, andthey extend lengthwise within the cover in generally parallel,side-by-side relation with each other. The shape of the inner cavity ofthe cover 11 is defined by the inner surface of the cover wall 1.6 andgenerally corresponds to the exterior shape of thecover `11; and thewall 16, through contact with outer onesof the wires 12, constrains themto a relationship in agences which mutual contact of the sheaths 19 ofneighboring wires 12 is close and intimate throughout their lengthwithin the cover 11. r1`he cross-sectional shape of the group or core ofwires 12 thus also corresponds, as seen in FIGURE 3, to that of theexterior of the cover 11.

The materials of the cover 11 are selected to produce a rigid, unitarystructure of excellent dielectric properties and resistance to high andlow temperatures and to abrasion. For these purposes, the wall 16preferably is made of dielectric fibers (for example, a glass fibercloth) impregnated with a hard-curing resin. The resin preferably isadhesively incompatible with the material of the sheaths 19 provided onthe conductors 20. Other of its qualities being in accordance with therequirements stated herein, it is entirely suitable that the resin be ofthe thermo-setting or heat-curing variety. For a cable intended foroperation at temperatures ranging from, for instance, -65 F. to 200 F.,a woven glass fabric meeting the requirements of U.S. GovernmentSpecification MIL-F-9084 and impregnated with a polyester-type resinconforming to Specification MIL-R-7575, Type II is suitable. Adequatematerials for a cover 11 made for use throughout a greater temperaturerange, for instance from -65 F. to 500 F. or above, include a glasscloth conforming to Specification MIL-Y-1140, No. 181 or 182 and a resinmeeting the requirements of Specification MlL-R-9299, Type II. The outersurface of the cover wall 16 preferably is smooth, while its innersurface complements the shape of the group of conductors 20 andcompensates for variations between the shape of the group and the outershape of the cover 11. The materials listed are given to providespecific examples of acceptable materials, and still others are entirelysuitable.

The term "rigid, as employed in Athe mechanical sense, has beenauthoritatively defined as absolutely invariable in shape and size underthe application of force. Because literally absolute invariability ofthe dimensions of concrete, physically real bodies under the applicationof forces is not to be found, the strictly applied term probably ismeaningful only in the abstract. It is commonly used, however, todesignate a body whose variation and size, deflection along its length,etc. is perhaps measurable but yet is so small as to be of no practicalinterest 0r significance when the body is loaded by forces within agiven and expectable range of magnitudes. It is in this latter sensethat the term rigid is employed in connection with multiconductor cable.Other terms employed herein, for example, dielectric, non-resonant,nonconductive, etc. are similarly employed in their common, practicalsense rather than in their absolute sense. The construction of themulticonductor cable 10 described herein provides it with a superiorrigidity which is importantly contributed to by the dielectric cover 11;and the latter, of course, is subject to stresses imposed upon the cable10 by bending loads. Forces urging deflections of the multiconductorcable generally are most apt to cause ultimate cracking or other failureof the cover at relatively pronounced bends in the cable, such as at 140r 15 in FIGURE 1, the deflections urged are such as would increase ordiminish the sharpness of the particular bend.

To reinforce and add to the rigidity of the multiconductor cable at, forexample, the bend 14, there is provided the construction shown inFIGURES 2 and 4. The wall of the cover 1:1, in the example shown, ismade up of at least two plies of resin-impregnated fabric. The inner ply(or plies) is made to lie closely along the wires 12 which the cover 11encloses; and in each of a facing pair of sides 27, 28 of the wall ofthe cover 11, a plate 29, preferably made of a light, strong metal andof such thickness and width as required for adding the neededreinforcement to the bent portion of the cable, overlies the inner ply23 within and preferably somewhat beyond each end of the bend 14. Theouter ply (or plies) 24 of the cover 11 separates from the inner ply 23at one end of the plate 29, passes tightly over the latter, and rejoinsthe inner ply 23 at the other end of the plate. It will be understoodthat, except where they are separated by the plate 29, the inner andouter plies preferably are merged into a unied, continuous wallstructure and in FIGURE 4 are shown as sharply delineated from eachother, merely to aid in providing an understanding of the relationshipexplained in the present paragraph. The plate 29 preferably is narrowerthan the outer dimension of the respective side 25 or 26 which itreinforces, and thus the entire plate is enclosed between the inner andouter plies 23, 24. Rigid bonding of the plies 23, 24 of the Cover 11 isensured by providing, in the plate 29, a liberal number of holes 30which are lled as at 31 with resin of the cover 11 and through whichresin in the outer ply 2d is continuous with resin of the inner ply 23.Addition of the plates 29 necessarily adds to the thickness of the coversides 25, 26 receiving them, and it is preferable that this addedthickness result in an increase of the over-all width of the exteriordimensions of the cover 11 rather than that the inner surface of thewall of the cover 11 be displaced inwardly to any extent causing anyexcess of compressive deformation, as discussed above, of the sheatns onthe wires 12. Reinforcement of the bend 14 is shown and described by wayof illustration, and similar reinforcement of course may be employed atother portions, such as at 15, or may be omitted altogether Wherevibrations, etc. to which the cable is submitted are not excessivelyheavy or severe.

It will be understood that for clarity of representation, thethicknesses of the plate 29 `and of the wall of the cover 11 have beenexaggerated, in the drawing, beyond the thickness generally preferred.For the same reason, the wall thickness of the individual sheaths 19 inthe wires 12 preferably are much thinner and the diameters of theconductors 20 often are much less than shown; and a smaller number ofwires -12 has been represented than frequently are employed within oneCover 11. Certain useages of the multiconductor cable 10 have been foundto require 250 or more wires 12 within a single cover 11; and many morecan be employed where desired since the diiculty or impossibility ofpulling a multitude of wires through a light-weight cover is eliminatedin the present invention.

Thus far, the multiconductor cable 1@ has been described as if it wereelongated, bent as at 14, 15 or wherever necessary to shape it to fitproperly along its intended route, and typified as having two ends 17,18 between which there are no branches. The multiconductor cable 10`indeed may be made in just such manner; but an importantly advantageousfeature of the cable 10 is that it may be provided with integralbranches as required for dividing the wires 12 and running differentones of them to different locations. With reference also to FIGURE 6 anddesignating the part of the cover 11 extending between the ends 17, 18as a first wall or cover portion 32, the multiconductor cable 13 shownby way of example is provided with a second wall or cover portion 33which is continuous with and which branches off `at an angle from theiirst portion 32 at a point between the two ends 17, 18 of the firstcover portion. As explained, the inner cavity of the `cover 11 extendsthrough the irst cover portion 32, including the bends 14, 15, from oneof its ends 17 to the other end 1S. The second cover portion 33 isintegral with the iirst portion 32 and in all important respects made inexactly the same way and as the latter; and the inner cavity of thecover portion 32 branches into the second cover portion 33 and extendsto its outer end 34. The cross-section of the first cover portion 32shown in FIGURE 3 is generally typical of crosssections which might betaken within the length of the second portion 33, and the interiorcavity is bounded at all locati-ons within both portions 32, 33 by theinner surface of the cover Wall 16.

The ends 17, 18, 34 of the iirst and second cover por.-`

tions 32, 33 define openings providing communication between theexterior of the cover portions 32, y33 and the elongated, branchedcavity within it. The wires 12 within the cover cavity extend outwardlybeyond the cover ends 17, 18, 34 to electrical connectors, such as 13,with which they may be provided, as required, at their ends. Wires 12entering the cover through a first opening at, for instance, the end 17extend through and out of the cover 11 through a second opening definedby another end 17. Again, some wires 12 may, as at 35, enter the outerend of the branch 33 and pass into the first portion 32 and towardeither end 17 or 18 of the cover. Voids which would be left, as at 36,within the cover interior where a group of wires is deected from astraight course to pass from one cover portion 32 or 33 to anotherpreferably iare filled by the complementary local thickening 36 of thewall of the cover 11.

The interchange of wires 12 from the first cover portion 32 to thebranch 33 will in some cases result in there being a smaller number ofwires in the cover first portion 32 on one side of the location wherethe second portion 33 branches from it than in it on the other side ofthis location. In this event, the dimensions of the cover 11 preferablyshould be reduced, as at 37 (FIGURE 7) in the side where there is thesmaller number of wires 12 until the inner cavity within that side issufciently small to maintain the wires 12 in the previously described,closely compacted relationship wherein the sheath of each wire 12 is inclose, intimate contact with the sheaths of other wires 12 throughoutits length enclosed in the cover 11.

In some cases, a separate branch of the cover 11, such as 33, will notbe needed or desired where one or more wires leave the cover 11 as atsome point between its ends 17, 18. In this event, a breakout opening39, that is, a wall opening through which a desired group 39 of thewires 12 may leave the cover 11, is provided. To prevent local weakeningof the cover 11 at the breakout opening 38, it is preferable that thelatter be made in a raised boss 4t? which is integral with and formed ofthe same materials as the remainder of the cover 11. The breakoutopening 38 is made of a size to enclose snugly the wires 39 which passthrough it, and it communicates with the interior cavity of the cover11.

Since the wires 12 are constrained to lie in a compact group having aminimum cross-section where they are within the cover 11, and since thisconstraint is lacking in segments of the group of wires 12 which extendoutside the cover 11, the wires 12 lying in contact with the cover 11where they leave an opening in the latter (for example, at the breakoutopening 3S or at the openings through which the wires extend at the ends17, 18, 34 of the cover 11) would be apt to be subjected to a localizedand possibly excessive pressure imposed upon them by the edge of thecover 11 deiining the opening if the transition from the fullyconstrained to the relatively unconstrained state were over-abrupt. Tomeet this diiiiculty, which is generally more severe where the wires 12must experience iiexure at the particular opening, a construction isprovided whereby the wires pass from the fully constrained state towardthe unconstrained state while they still are enclosed within the cover11. Thus, for example, a iiare 66 (FIGURE ll) is provided in the innercavity of the cover 11 at its end 1S (FIGURES l and ll), and similarenlargement of the cross-section of the cover 11 may be employed asneeded at other of its openings, for example, at the opening 3S throughthe boss 40.

For protection of the'wires 12 where they extend outside the cover, itis in many cases desirable to protect them with a flexible outer jacketwhich lies in encasing relation to them. As a feature of the invention,the breakout opening 38 or any of the other openings at the ends 17, 18,34, of the cover 11 are provided as desired with a flexible jacket 41mounted in the particular opening in firm attachment to the cover 11. Apreferred material for the flexible jacltet 41 is a tube 43 made oftetraiiuorethylene and provided with a convolution or spiral corrugation42 (FIGURE 7) which runs, in the manner of a screw thread, from one endof the jacket to the other. The tetratiuorethylene tube 43 preferably iscovered with a glass fiber cloth 44, which conforms to the convolutedcontour of the tube 43. Such a jacket 41, because of its Teflon"interior, has very little abrasive effect on the wires 12 within it uponbending and deflections that cause its wall to rub on the wires, and theglass cloth exterior has good resistance to abrasion. The jacket 41readily yields and shows good flexibility when there is imposed upon itforces tending to lengthen, compress, or bend it. The glass fiber outerlayer 44 of the outer, flexible jacket 41 interlocks firmly with andbecomes integral with the wall of the cover 11, and the latter islocally thickened to fill the convolution 42 and thus ensure anexcellently secure mounting of the flexible jacket 41 in the end of thecover 11. Where the jacket 41 must withstand high temperatures, itshould be made of temperature-resistant materials; and those suggestedabove are adequate in t-his respect. While a flexible outer jacket 41 isshown only for the wires 35 extending from the outer end of the secondportion or branch 33 of the cover 11, it may similarly be employed atany opening of the cover, including the breakout opening 38.

Where a flexible section is desired within the length of themulticonductor `cable 10, such may be provided by terminating the cover11 (FIGURE l) at one end of the desired flexible section .45 andemploying a second cover 46 which is spaced from the first and whichreencases the wires 12 where, at the other end of the ilexible section45, they pass into the second cover 46 through the opening defined atits end 34 by the wall of the cover 11. The second cover 46 `may beconstructed in the same general manner and of the same materials as thefirst cover 11. The wires 12 pass through its interior cavity and areconstrained to the same relation with each other and the second cover 46as described in connection with the first cover 11. This construction isof excellent usefulness, for instance, where the first cover 11 ismounted, by any suitable clamping means 47 or equivalent, on a structure48 which is subjected to vibratory or other movements relative toanother structure 49 on which the second cover 46 is mounted. It ispreferred that the bundle of wires 12 in the flexible section 45 lyingbetween the first and second covers 11, 46 be twisted as a group, forthis greatly enhances the flexibility of the group of Wires 12 wherethey lie outside the covers 11, 46. For the same reason, the groups ofwires 12 leaving the other openings of the covers 11, 46 also may betwisted. Although it has been omitted from the drawing in order to showthe wires in the flexible section 45 between the first and second covers11, 46, the wires in the flexible section 45 preferably are covered by aflexible outer jacket which is similar to that shown at 41 at the outerend 34 of the first cover branch 33 and which has each of its endsmounted in a respective end of the first or second cover 11, 46 in themanner in which, as shown in FIG- URE 6, an end of the jacket 41 ismounted in the end opening of the branch 33.

The multiconductor cable described above may be made in any way known orwhich may be devised which will produce the article described. Onemethod, for instance, includes laying up into -a harness the desiredwires 12 which are to be included in the cable 10 and then covering themwith a substantially rigid tubing made of one of the variouspre-stressed plastics which will shrink upon being heated above itsthermal relaxation temperature. By the controlled application of heat,then, the outer tubing enclosing the harness maybe caused to contractand compact the wires 12 to the condition and relationships previouslydescribed.

According to a preferred method of making the multiconductor cable,however, the wires *1'2 which it is desired to include in it are builtup into a harness 50 as shown in FIGURE 8. The Wires 12 employed shouldof course conform to the requirements as to materials, etc. set forth inprevious paragraphs. The wires 12 preferably should not be marked bystamping since this tends to cause mechanical and electrical weakeningof the insulating sheaths of the wires. Care should be taken thatneither the conductor 20 (FIGURE 5) or the insulating sheath 19 of anywire 12 used is broken, cut, or nicked. Assembly of the wires 12 shouldbe such as to produce a harness 50 of a shape which generally fits theapplicable mold 51 (FIGURES 9, 10) in which, as will be described, theharness 50 is brought to its final, desired shape. Since the intricaciesof assembly of a wire harness are well known in the art, no furtherdescription of this step is required beyond mentioning that theharnessS0 preferably is held together by mechanical means such as, forinstance, temporary spot ties of twine 52 made at, for example, 10- to12inch intervals along the harness 50 and preferably removed therefromprior to the step of molding described below. In the completed harness50, wires which are intended to pass through a break-out opening 38(FIGURE l) or into a branch 33 of the multiconductor cable 10 shouldbranch away from the main body of the harness 50 (FIGURE 8)approximately as they will inthe completed cable. Within the harness 50,the wires 12 should lie as nearly as practicable in parallel relation toeach other, and excessive crossing of wires should be avoided, thoughsome crossing of the wires 12 is acceptable and generally will notdiminish the quality of the finished cable.

The mold 51 (FIGURES 9, 10) employed for making the multiconductor cableshould be shaped, branched, etc. as required to cause the materials ofthe cable 10, when formed in it, to have the shape desired at all pointsin the finished article. Deviations from plane surfaces on themulticonductor cable 10 are best made on its upper side 25 (FIGURE l)since it is generally more feasible to make corresponding variations inthe surface of the male part 53 of the mold 51 which forms this side 25of the cable 10. The mold 51 shown in FIGURE 9, for example, is intendedfor making a multiconductor cable 10 of square or rectangularcross-section as shown in FIGURES l and 3. Accordingly, the female part54 of the mold 51 (FIGURE 9) contains a channel Whose three sides 55,56, 57 have the shape and dimensions of the three sides 26, 27, 28 ofthe cable 10 (FIGURES 1 and 3), and the lower surface of the male piece53 of the mold is shaped and dimensioned to correspond to the remaining,upper side 25 of the cable. Similarly, the parts of the complete mold 51(FIGURE l0) are bent as at 58 and 59 and branched as at 60 incorrespondence with the bend 14 and 15 and branch 33 of the completedmulticonductor cable 10 (FIGURE l). Whereas one mold section 51 withmale and female parts 53, 54 is used for making the first section '11 ofthe cable 10, a second mold section 61, spaced from the first by aninterval equal to the length of the flexible section 45, is employed forthe second section 46 of the cable.

The impregnated fabric previously described is wrapped about the harness50, or, according to a preferred procedure, it is laid up in the femalemold sections to form a lining in the latter as shown at 62 in FIGURE 9.The width of the material 62 should be sufficient to provide an overlapof its edges 63, 64 when, as will be described, it is folded over thewires 12. As many plies of the fabric 62 as required should be employedfor making a cover Wall thickness. Since this requirement will vary withthe fabric employed and with the cross-section and other dimensions ofthe cable to be made, and since 11 or 46 (FIGURE l) with adequate' knowntechnics laying up impregnated bers in molds are well developed,specific instructions will not be given in regard to the number of pliesto be used nor of the manner of laying them one over the other since oneskilled in the art can readily proceed without such direction. Severalprocedures peculiar to the making of the multiconductor cable requirespecific explanation, however, in connection with laying the materialsof the cover 11 in the mold female parts 54, and these explanationsfollow.

Where required at bends in the cable, as at 14 (FIGURE l), thereinforcing plate 29 (FIGURES 2, 4) is introduced during the laying upof the impregnated cloth 62 in the molds. At least the outer ply orplies 24 of the cloth 612 are laid in the mold female part 54, then theplate 29 is set in place. Next, the inner ply or plies 23 are laid upover the plate 29 to produce the relation shown in FIGURE 4 betweenouter plies 24, plate 29, and inner plies 23. lf the cloth 62 is notheavily enough impregnated to ensure filling of the holes 30 of theplate 29 with resin 31 when the wires 12 and cloth 62 are placed underpressure in the mold, it is helpful, for securing best bonding of theplate 29 with the cover 11, to add more resin locally, as needed, at theplate 29 for complete filling of the holes 30.

If a flexible jacket 41 is to be employed in the multiconductor cable 10at one of the openings of the cover 11, a piece of tubing, preferably ofthe kind described above and shown at 41 in FIGURE 8, is placed on thepart of the harness 50 which will lie at the opening concerned. Otherjackets such as 41 similarly are placed as desired on the harness 50 atlocations corresponding to other openings of the cover 11.

With the lay-up of the impregnated cloth 62 complete, and with the edges63, 64 of the cloth laid aside, for example as shown in FIGURE 9, thewire harness 50 is laid in it within the mold female part 54 and theedges 63, 64 of the cloth are folded over the wires 12 and lapped overeach other as shown in dotted lines in the drawing. jacket or jackets41, if such are employed in the particular multiconductor cable 10 underconstruction, are checked for location and slipped along the harness 50as necessary to bring them into proper overlapping relationship with thematerial of the cover 11 at the cover opening or openings involved asshown in FIGURE 8.

The male part 53 of the mold then is brought down on the cloth-wrappedwires 12 with pressure enough to compact and form them and material ofthe cover 11 to the shape and relationships with each other previouslydescribed. Any gaps which occur between ones of the wires 12 lying nextto the cover 11V are lled in the molding process by resin and fabricsqueezed into them as at 65 in FIGURE 3; thus, Vthe inner surface of thecover lll complements the outer periphery of the group of conductors 12,and the outer surface of the cover |11 is smooth and of a shapepredetermined by the shape of the mold parts 54, 55.

The molded .multiconductor cable 10 is kept under pressure in the molds51, 61 until the resin of the cover 11 has set and solidified to asubstantially rigid, dimensionally stable state. Where a thermosettingresin is employed in the cover 1.1, the curing should of course be doneduring the application of heat to the cable 10 while it is retained inthe mold. The temperature employed should be appropriate for propercuring of the resin and should not be high enough to be a factorresulting in permanent dimensional or other changes in the individualinsulating sheaths 19 of the conductors 20. When the cover `11 isproperly cured, the cable 1t) is removed from the mold. Some or all ofthe plugs 13 or other connectors or terminals provided on the wires 12may be added ,thereto before the molding step, or, as may be expedient,they may be added after the wires 12 are molded into the cover or coversBefore or as this is done, the flexible 11, 46', the latter mode ofprocedure being preferred in the majority of instances.

The multiconductor cable 10 whose form and mode of construction asdescribed above is of superior low weight l and volume since theindividual sheaths 19 of the conductors 20 preferably contain only theamount of material necessary, with adequate safety margin, forpreventing shorting and arc-over between the wires 12 and since theweight of individual abrasion-resistant covers on the wires iseliminated, the cover 11 providing excellent abrasion protection, atgreat saving in weight, for all the wires 12. The wires 12 preferablyare held by the cover 11 in as close association with each other as ispractically possible without so deforming the individual insulatingsheaths 19 of the wires 12 by excessive wire-to-wire pressures thattheir insulating ability would be significantly reduced; consequently,they are held by the cover 11 in a group of as high a density and low avolume as is practically possible. Pre-shaped by the molding process,the cable 10 conforms to the surfaces of bodies such as 4S, 49 againstor near which it is designed to be mounted; of rigid construction, it isnot deectable when clamped to a xed body and consequently remains in axed, accurately known location relative to that and other bodies ofaccurately predictable position.

Several factors combine to make the multiconductor cable 10substantially non-resonant to mechanical vibrations. The cover 11,because of the materials of which it is made, is inclined to berelatively free of resonance. Within this cover 11, the wires 12 lie ingenerally parallel relation to each other, and adjoining wires 12 areclosely in contact with each other. Upon the cable 10 being subjected toa vibratory force which tends to make it oscillate in resonance with thevibration, any deection of the `cable 10 away from its normal positionwould cause a small bending of the cable 10. Wires of the cable 10 atthe outside of the bend would tend to be stretched and wires on theinside to be compressed. Because of their low coefficient of friction,the wires 12 in such case slide yupon each other, thus expending much ofthe energy that causes the bending in friction losses and making itunavailable for causing a rebound to and/or beyond the normal positionof the cable 10. The multiconductor cable 10 thus is non-resonant ascompared with a cable in which the wires are all embedded in one commonblock of insulating material or in which their coeicient of friction isso high that the individually insulated wires are bound to each other byfriction and behave as if enclosed by a solid block of insulatingmaterial; for, in such a construction, the energy expended in forcing acable segment through one lhalf-cycle of avibratory motion is stored inthe material of the wires and their insulating sheaths and suppliesenergy causing or aiding the cable to move through the next half-cycleof vibration. Previous cables, for this reason, have had to be clampedat quite close intervals to prevent the formation of standing waveswhich otherwise would form as the cables came into resonance withvibrations of bodies on which they might be mounted. Because of itsrigidity, which prevents its drooping or sagging between clamps, andbecause of its substantial freedom from resonance with vibrations of theobjects with which it -is associated, the multiconductor cable 10requires a quite favorably small number of clamps 47, and these may bespaced `at Wide intervals; thus, the cable 10 is much more easily,quickly, and in expensively mounted than previously employed cables.

Wel-l able to withstand abrasion, blows, etc. because of its hard, roughcover 11, the multiconductor `cable 10 has greatly improved resistanceto electrical overloading of its wires 12. When an excessive current ispassed through one or several of the wires 12, they of course tend tooverheat. are, however, (among the class of resilient insulatingmatenials) fair conductors of heat, while the metallic conductors 20 arethemselves excellent heat conductors.

The individual sheaths 19 of the conductors Each wire 12 is preferablyin intimate contact, all along its length, with other wires 12; andthese other wires act l.as heat sinks which carry oil the excessive heatproduced by overloaded ones of the wires. If a wire 12 is overloaded sogreatly that it eventually fails, the heat-sink relationship between thewires 12 prevents failure within the cover 11; and it is a greatadvantage of the multiconductor cable that the failure consistentlyoccurs outside the cover 11 at the uncovered, accessible ends of thewires. In the same manner, a segment of the cable 10 locally exposed towhat would otherwise tend to be excessive ambient temperatures is cooledby the heat-sink action of other segments of the cable located in coolerareas. High `ambient temperatures and/ or heavy electrical loading ofthe entire cable is well withstood by virtue of the heat-resistantmaterials of the cover 11 and of the individual insulating sheaths 19 ofthe wires 12. The multiconductor cable 10, when made of the materialssuggested, furthermore may easily be made substantially water-proof andairtight, and itis substantially immune to the effects of acids `andbases and their reaction products. It thus is able to stand up well inchemical environments in which other cables could not survive. For thisreason, the multiconductor cable is excellent, for example, for useunderground as well as in many other applications including thosepreviously mentioned.

While only one embodiment of the invention has been described herein andshown in the accompanying drawing, it will be evident that variousmodifications are possible in the arrangement and construction and inthe method of making the multiconductor cable without departing from thescope of the invention.

I claim:

l. A multiconductor cable comprising: individually insulated, elongatedconductors; a tubular, rigid, one-piece cover made of a dielectricmaterial molded about the conductors and having a wall, the coverfurther having an elongated inner volume enclosed by the wall, t-heconductors -being compactly grouped together within and extending along`the length of the inner volume of the cover and lying in generallyparallel relation with each other, the conductors tightly filling thecover inner volume and being confined through contact of at least someof the conductors with the Wall in a relationship wherein substantiallyevery one of the insulated conductors, throughout subst-antially all itsextension through the interior volume of the cover, has mechanicalcontact with others of the insulated conductors.

2. A multiconductor cable comprising: a plurality of elongatedconductors lying in generally parallel relation with each other; aplurality of individual, resilient, insulating sheaths, substantiallyevery one of the conductors being individually covered by a respectiveone of the sheaths; and a rigid, tubular, dielectric, unitary covermolded about the conductors and sheaths, the cover having a wallenclosing an interior volume substantially completely filled by theconductors andA of a smallness sufficient to maintain substantiallyevery one of the sheaths in close contact with others of said sheathsthroughout substantially all their coextension through the ,interiorvolume of the cover.

3. A high-density multiconductor cable comprising: a

vplurality of elongated conductors having individual insulating sheathsand lying in generally side-by-side, parallel relation with each other;a substantially rigid cover molded about the conductors, the cover beingof predetermined outer shape in cross-section and having a wall made ofa dielectric material of high abrasion resistance, the wall enclosing anelongated cavity and constraining the insulating sheaths to a closelycontacting, compacted relation with each other, the conductors beinggrouped to form a core with an outer cross-sectional shape generallycorresponding to that of the cover and substantially filling theelongated cavity of the cover, the thickness of the cover Wall beingvaried inwardly of the cavity 14 in eomplernentto variations in thecross-.sectional shape of the core and in compensation for anydilferences between that shape and the outer shape in cross-section ofthe cover. l

4. A multiconductor cable comprising: a pluralityof elongated conductorslying in generally parallel relation with each other; a plurality ofsheaths, each of the sheaths being on a respectiveone of the conductors,the sheaths being made of a resilient, heat-conductive, dielectricmaterial; and means for maintaining said conductors in heatexchangingrelation with each other, said means including a rigid, tubular, untarycover having a wall molded about the sheathed conductors and enclosingan elongated interior volume of the cover substantially filled by theconductors and of a smallness suficient to maintain substantially everyone of said sheaths in intimate contact, throughout substantially allits respective length within the interior volume of the cover, withothers of said sheaths.

5. A non-resonant, substantially rigid multiconductor cable comprising:a plurality of elongated conductors disposed gener-ally parallel to eachother; a plurality of sheaths of tubular, single-layered construction,each of the sheaths being on a respective one of the conductors and madeof a dielectric material substantially free of adhesive compatibilitywith the materials of the cover; a substantially rigid, electricallynon-conductive cover comprising a wall molded about the sheathedconductors and made of dielectric fibers impregnated with resin, theconductors being confined by the wall through contact of the latter withat least some of the sheaths to a relationship wherein substantiallyevery one of the sheaths, throughout substantially all its length Withinthe cover, has intimate contact with others of the sheaths, the materialof the sheaths having a coeiiicient of friction small enough to permit,upon lexure of the cable, a sliding of ones of said sheaths along othersof said sheaths with which they are in contact within the cover.

6. A high-density, low-weight, temperature-resistant multiconductorcable highly immune to abrasion, said cable comprising: a plurality ofelongated conductors; a respective sheath on each of the conductors, thesheaths being made entirely of a resilient, temperature-resistantplastic and being of minimum thickness for safely preventing arc-overbetween adjoining ones of the conductors when the conductors aresubjected to intended service voltages; a rigid, electricallynon-conductive cover comprising a wall molded about the sheathedconductors and made of a dielectric, temperature-resistant, hard-curingresin reinforced with inorganic fiber, a plurality of elongatedconductors disposed generally parallel to each other and along thelength of the cover within the interior cavity of the latter; and arespective sheath on each of the conductors, the sheaths being made of aresilient, temperature-resistant plastic and being of minimum thicknessfor safely preventing arc-over between adjoining ones of the conductorswhen the conductors are subjected to intended service voltages, theinterior dimensions of the cover being substantially completely filledby the sheathed conductors and of interior dimensions small enough toprovide a constant, inwardly imposed constraint on substantially all ofthe conductors along substantially all the length of the cover throughcontacts which exist between the cover wall and sheaths of theconductors, said constraint being suticient to hold substantially everyone of the sheaths, throughout its length lying within the interiorcavity of the cover, in close contact with others of the sheaths.

7. A multiconductor cable comprising: a rigid, elongated, one-piececover having two ends and made of a dielectric material, said coverhaving a wall with an outer surface and enclosing a cavity extendingbetween the two ends of the cover, said cover having between its twoends a bent portion through which the cavity extends; a plurality ofelongated conductors with individual, di-

electric sheaths, the conductors and sheaths substantially completelyfilling the elongated cavity, the wall extending around the conductorsin a closely contacting relationship therewith which maintains theconductors in closely packed, substantially parallel relation with eachother; and a metallic plate disposed between the conductors and theouter surface of the cover at the bend of the latter, the metallic platebeing rigidly bonded to the cover and the cover being molded about theconductors.

8. The cable defined in claim 7, the cover comprising inner and outerlayers of an inorganic fabric and a cured resin impregnating the layers,and the metallic plate being disposed between inner `and outer layers ofthe fabric and being pierced with a plurality of holes filled with resincontinuous with resin impregnating the layers of the fabric.

9. A multiconductor cable comprising: individually insulated, elongatedconductors; a tubular, rigid, unitary cover having a wall molded aboutthe conductors, the wall being made of a dielectric material and havingtwo ends; and a breakout opening formed in the Wall between said twoends and communicating between the exterior and interior of the cover,some of the conductors extending out of the cover interior through thebreakout opening, the conductors, where they lie within the cover, beingconfined, by co-ntact of at least some of the conductors with the wall,in a compactly grouped, generally parallel relationship whereinsubstantially every one of the conductors, throughout substantially allits length lying within the cover, has close contact with others of theconductors.

10. A multiconductor cable comprising: a tubular, unitary cover having awall including a first wall portion with two ends and a second wallportion continuous with and extending at an angle from the first wallportion at a place between the two ends of the latter, the first wallportion enclosing a first elongated, interior cavity extending betweenthe two ends of the rst wall portion and the second wall portionenclosing a second elongated, interior cavity continuous with andbranching from the first; individually insulated, elongated conductorshaving extension within and lengthwise of the first interior cavity ofthe cover, the conductors being compactly grouped in generally parallelrelationship where they lie within the first interior cavity of thecover, some of the conductors extending out or" the first into and alongthe second interior cavity, the conductors, where they lie within theirst and second interior cavities, being confined, by contact of atieast some of the conductors with the cover wall, in a relationshipwherein substantially every one of the conductors, throughoutsubstantially all its length lying within the cover, has close contactwith others of the conductors, the cover being made of a rigid,dielectric material molded about the conductors.

11. The multiconductor cable claimed in claim 10, at least one of thewall portions having formed therein, within its length, a breakoutopening communicating between one of the interior cavities and theexterior of the cover, some of the conductors extending out of one ofthe interior cavities through the breakout opening.

12. A multiconductor cable comprising: a tubular, rigid, unitary coverhaving a wall enclosing an elongated interior cavity and definingopenings communicating between the interior cavity and the exterior ofthe cover; a plurality of individually insulated, elongated conductorsentering the interior cavity through a first one of the openings andleaving the cavity through at least a second one of the openings, atiexible, tubular, dielectric jacket firmly mounted in at least one ofthe openings and in encasing relationship to ones of the conductorspassing through that opening, the jacket extending outwardly of thecover from the opening, the conductors, where they lie Within theinterior cavity, by contact of at least some of them with the wall,being confined in a relationship wherein substantially every one of theconductors, throughout substantially all its length lying within theinterior cavity of the cover, has close contact with others of theconductors, the cover being made of a rigid, dielectric material moldedabout the conductors.

13. The multiconductor cable claimed in claim l2, the cable furtherincluding a second, tubular, rigid, unitary cover made of dielectricmaterials and spaced from the cover called for in claim l2 by aninterval, the second cover having a wall enclosing an elongated cavityand defining an opening communicating between the exterior and theinterior cavity of the second cover, at least some of the conductorspassing through the opening of the second cover and extending within andalong its interior cavity, the conductors, by contact of at least someof said conductors with the wall of the second cover, being conned in agenerally parallel relationship with each other wherein substantialiyevery one of said conductors, along substantially all its length lyingwithin the interior cavity of the second cover, has close contact withothers of the conductors, the conductors which pass through the openingof the second cover being twisted together throughout the intervalseparating the two covers and passing through one of the openings of thecover called for in claim 12. t

14. A high-density multiconductor cable comprising: a plurality ofelongated conductors having individual insulating sheaths and lying ingenerally side-by-side, parallel relation with each other; asubstantially rigid cover molded about the conductors, the cover beingof predetermined outer shape in cross-section and having a wall made ofa dielectric material, the wall enclosing an elongated cavity andconstraining the insulating sheaths to a closely contacting, compactedrelation with each other, the conductors being grouped to form a corewith an outer cross-sectional shape generally corresponding to that ofthe cover and substantially lling the elongated cavity of the cover, thecover having at least one end provided with an opening through whichVsaid conductors extend out of said cavity and the cover wall havingadjacent said opening an outwardly flared portion wherein the wall, atsuccessive points approaching the opening, exerts progressively lessconstraint on the conductors, whereby there is a progressive transitionbetween the closely compacted relation of the conductors inside thecover and a less closely compacted relation of the conductors where theylie outside the cover.

References Cited in the tile of this patent UNITED STATES PATENTS1,574,297 Lilleberg Feb. 23, 1926 2,166,420 Robertson July 18, 19392,299,140 Hanson Oct. 20, 1942 2,658,014 Morrrison Nov. 3, 19532,883,314 Martin Apr. 21, 1959 OTHER REFERENCES Publication i,Orangeburg Fibre Conduit, published in Electrical Construction andMaintenance, August v1953 (page 56 relied on).

